The present invention relates generally to plastic parts made by injection molding, and more specifically to such parts having two distinct regions typically delineated by distinct colors or distinct types or grades of plastic, and a method for making same.
It is common in conventional molding technology to produce molded parts having two colors or two types of plastic by a technique referred to as overmolding. First, a base part or frame is produced in a first injection mold, and the resulting base part is designed to have recesses, cavities, channels, etc., referred to as “voids” that will ultimately accommodate the second color and/or grade of plastic. This base part is then placed in a second mold, in which the second color/grade of plastic is injected such that the molten plastic fills the previously created voids.
This type of overmolding is fairly common on many types of consumer products, including tooth brushes, kitchen utensils and grips of hand tools, and achieves satisfactory results. However, when applied to products subjected to more severe operational environments, such as where significant part flexing occurs, it has been found that the parts often separate at the junction of the two types of plastic. Also, in other cases, one of the types of plastic has a relatively larger amount of dimensional instability, causing eventual delamination of the finished part.